1. Field of the Invention
The present invention relates to a flow control device for controlling the flow of various kinds of fluids. Specifically, the present invention relates to a valve mechanism for the flow control device.
2. Description of Related Art
For a valve mechanism used in a flow control device for controlling the flow of LP (liquefied petroleum) gas, town gas, coolant for a refrigerator or an air-conditioner, or liquid, a needle system, a disk system, or a ball system is typically used.
A conventional valve mechanism of a needle system is superior in a linear adjustment function of the flow rate but is liable to be expensive because a high degree of accuracy is required for respective mechanical components to obtain a completely closed state. Further, since a mechanism for converting the rotary motion outputted from a motor into linear-motion is required, the energy conversion efficiency is low and the durability is poor. In addition, since the needle closes like a wedge in the closed state, large energy is required to change from the closed state to the opened state.
A conventional valve mechanism of a disk system is superior in a linear adjustment function of the flow rate and has an advantage that arbitrary flow patterns can be easily realized. However, in order to realize a completely closed state, the flatness with not more than 1 μm, that is, the degree of the surface roughness nearly equal to a mirror plane is required for the accuracy of facing surfaces, which increases the cost. Further, large energy is required to drive highly accurate surfaces contacting with each other, because an adsorption phenomenon between the contacting surfaces is easy to occur. In addition, in general, the diameter of the aperture, to which the disk system is applied, is limited to a small size, for example, not more than 2φ, i.e., 2 mm in diameter.
A conventional valve mechanism of a ball system can easily realize the completely closed state but is difficult to realize the linear adjustment of the flow rate.
As described above, none of the conventional valve mechanisms is provided with both the linear adjustment of the flow rate and the completely closed function. In order to provide these functions in the conventional valve mechanisms, a precision within the μ (micron)-order is required in various components, which increases the cost of the overall mechanism. In particular, when the valve mechanism having a larger aperture part is provided with both the linear adjustment function of the flow rate and the completely closed function, the mechanism becomes expensive because the precision for the respective components is required to be further enhanced. Further, power savings and speeding up the control are difficult because driving the valve mechanism is accompanied with loss for converting rotational motion into linear motion and friction loss.